Previous research findings suggest that maths anxiety may mask an individual’s true maths ability. The overarching aim of the studies presented in the current thesis was to empirically study possible mechanisms underpinning the typically observed negative relationship between maths anxiety and maths performance. One of the main theoretical explanations for the relationship between maths anxiety and performance has focused on the influence of maths anxiety on working memory. In particular, processing efficiency theory (Eysenck & Calvo, 1992) accounts of anxiety effects refer to the role of worry in draining working memory resources, and other accounts also refer to potential problems with a deficient inhibition mechanism associated with intrusive thoughts. However, previous research has failed to adequately investigate a processing efficiency account of maths anxiety effects. Using self-report measures of maths anxiety and performance on two-digit addition verification tasks, the studies presented in this thesis attempt to address this, also taking into account the recent update to processing efficiency theory: attentional control theory (Eysenck, Santos, Derakshan & Calvo,2007). Initially, in order to address the question of whether there are neuropsychological correlates of maths anxiety, perhaps associated with increased activation within the frontal cortex, an experiment employing an electroencephalogram methodology was used to measure event-related potentials (ERPs) in response to mental arithmetic. Results showed no evidence for an effect of maths anxiety on ERPs. Despite this, the typical negative relationship between maths anxiety and performance was observed. The subsequent studies therefore attempted to investigate the mechanisms behind this. The next experimental study used a modified version of the Cognitive Intrusions Questionnaire (Freeston et al., 1993) to assess self-reported in-task intrusive thoughts. Maths anxiety was found to be related to specific task-related intrusive thoughts. In turn, some cognitive intrusions were related to performance. However, there was no evidence to suggest a joint relationship between maths anxiety and cognitive intrusions in explaining maths performance, providing little support for some of the existing explanations of maths anxiety effects. The third experimental study used a novel eye-tracking methodology to investigate the role of eye-movements in explaining the maths anxiety-to-performance relationship. However, maths anxiety was not found to moderate the relationship between eye-movement, e.g. fixations, dwell-time, and saccades, and performance, despite eye-movements being a strong predictor of performance. Across studies, and particularly on maths problems involving a carry operation, maths anxiety was found to be related to longer response times to correctly answered maths problems, with some inconsistency in error rates. Such maths anxiety-toperformance relationships are consistent with key assumptions of a processing efficiency and attentional control account of anxiety effects on performance. The exact mechanisms underpinning this relationship, however, remain unclear. In addition, the thesis reports on and presents a newly developed scale for measuring maths anxiety. The need for a new scale arose out of acknowledgement of validity issues with existing scales and the new Mathematics Anxiety Scale – U.K. has been shown to be both a reliable and valid tool for measuring maths anxiety in a British, and potentially European, undergraduate population.